Shortly before the Second World War time, Nishina reported on a series of prominent nuclear physical and radiochemical studies in collaboration with Kimura. They artificially produced 231Th, a member of the natural actinium series of nuclides, by bombarding thorium with fast neutrons. This resulted in the discovery of 237U, a new isotope of uranium, by bombarding uranium with fast neutrons, and confirmed that 237U disintegrates into element 93 with a mass number of 237.”